function __search_by_title_only($search, &$wp_query) {
    if (empty($search)) return $search; // skip processing - no search term in query
    $q = &$wp_query - >query_vars;
    // wp-includes/query.php line 2128 (version 3.1)
    $n = !empty($q['exact']) ? '': '%';
    $searchand = '';
    foreach((array) $q['search_terms'] as $term) {
        $term = esc_sql(like_escape($term));
        $search. = "{$searchand}($wpdb->posts.post_title LIKE '{$n}{$term}{$n}')";
        $searchand = ' AND ';
    }
    $term = esc_sql(like_escape($q['s']));
    if (empty($q['sentence']) && count($q['search_terms']) > 1 && $q['search_terms'][0] != $q['s']) $search. = " OR ($wpdb->posts.post_title LIKE '{$n}{$term}{$n}')";
    if (!empty($search)) {
        $search = " AND ({$search}) ";
        if (!is_user_logged_in()) $search. = " AND ($wpdb->posts.post_password = '') ";
    }
    return $search;
}
add_filter('posts_search', '__search_by_title_only', 10, 2);